ITU -R BT 601 (old name: CCIR 601 ) is a standard, the (now ITU -R) was published by the CCIR and specifies how interlaced digital video signals to be encoded. It contains methods for analog television signals with a frame rate of 60 Hz and 525 lines, or alternatively, to digitize at a frame rate of 50 Hz and 625 lines.
The timing of the CCIR-601 signal are similar to those of the analogous precursor, such that a transformation, both in the one and in the other direction is possible without great expense. There are thus also provided time ranges for the synchronization signals and blanking intervals of the analog signal. The pixel clock is independent of the frame rate of 13.5 MHz.
In the 50 -hertz version of the duration of a line is exactly as specified in the analog television signal to 64 microseconds, resulting in a nominal horizontal resolution of 864 pixels per line. Of the 64 microseconds 12 microseconds nor for the blanking signal must be subtracted. So stay 52 microseconds for the visible line. The active area of a line is 53 ⅓ microseconds (720 pixels ) is slightly wider than the standard analog with 52 microseconds (equivalent to 702 pixels). Also in the image height increases, the active region: there are now 576 visible lines instead of 574 whole and each half the top right and bottom left. When digitizing an analog signal, there is therefore little black edges.
The standard says nothing about whether and how a digital signal into an analog reconvert.
CCIR 601 goes on to say that the color signal values Cb and Cr of each second pixel are to be ignored. This color model is YCbCr -4: 2:2 called, according to the ratio of the three values of brightness, color deviation blue / yellow and red color deviation / turquoise. For two successive pixels, for the two brightness values Y1 and Y2 and the two color difference values in the order Cb: Y1: Cr: stored Y2. The brightness values of at least 8 bits to quantize the color difference values with at least 4 bits. In studio use, all values are quantized with the higher resolution of 10 bits.
At CCIR 601 (or more precisely: CCIR 656) the synchronization signals from the analog video signal are not transmitted digitized. Instead, the visible video area is marked by special digital synchronization signals the beginning ( SAV = Start of Active Video) and the end ( EAV = End of Active Video) signal of a video line. Between SAV and EAV the digitized video information is transmitted. The time ranges between EAV and SAV are either filled with meaningless content, or that it shows as digital audio data embedded. Such devices are called embedder. For 8- bit systems with the specially reserved values 0x00 (0) and 0xFF (255 ), the SAV and EAV signals in the form 0xFF, 0x00, 0x00, 0xYY coded. The value 0xYY is a bit field and define if it is a line beginning or end of a line, an image beginning or a fine, or a straight or odd field ( Field).
Obtaining the time of the horizontal and vertical blanking intervals in the digital data stream is necessary to ensure the temporal relationship between the analog video signal and the digital image shown. Without getting these areas the line frequency of the analog and digital video data would not match with the same frame rate, which would mean that in the conversion of a complete image would have to be buffered.
The first version of CCIR 601 defined only a parallel interface, but later versions introduced (better known as SDI), which are now commonly used, the bit - serial family of serial digital video signals. The 8 -bit serial protocol was previously used in the D1 digital tape recording. It also quantizes the color difference values with 8 bits and is referred to Y1: Y2: Cb1: Cr1 thus a data rate of
Modern standards use a Kodiertafel that adds one to two check bits. The 9 -bit serial version has a data rate of 243 Mbit / s The used in the D5 digital tape recording 10 -bit version has a data rate of 270 Mbit / s
There is an 8 -bit version, in which only the actual image area is transferred. This requires 165.9 Mbit / s
Since according to specification, the digital values are 0 and 255 used as a synchronization values , the valid luminance and color values range is reduced. Therefore, the luminance (Y) are 220 values available (16 ... 235 ) to an adequate buffer zone above and below the valid values to achieve. These areas are called Head and Foot Room, which serve to catch any (invalid ) overshoot, without compromising the synchronization. The chrominance ( Cb, Cr) is represented in each case on 225 valid values (16 ... 240), wherein the value defines the zero point 128 and thus to the colorless state of the two color signals. In this area, a pure black and white image, or a gray level can now be transferred.
The CCIR - 601 video raster format has been reused in several later standards, including MPEG. The FourCC identifier for a CCIR-601 data stream is V422.